This invention relates to a method of discriminating between front and reverse sides of a paper sheet and more particularly to a novel method of discriminating between the front and back sides and between upper and lower edges of the paper sheet with high precision through comparison of signal waveforms derived from the printed pattern design on the sheets as sensed at several portions of the paper sheets.
There are a variety of methods presently used for discriminating between the front and reverse sides of the paper sheet. According to a first method, when the paper sheet is a bank note issued by the Bank of Japan, it has marginal zones along the four edges on both the front and back sides, these zones being different in area for the front and back sides. Thus the difference in size of these marginal zones is detected by means of reflected light for discriminating whether the surface being sensed is in the front or back side.
With this known method, fluctuations in the reflected light may be caused due to contamination, breakage or folds of the marginal zones or to deflection or vibrations caused in the course of transport. The result is lowered precision in sensing and error caused in discrimination.
According to a second method, the difference in the pattern design on the front and back sides of the paper sheet is detected in terms of the difference in the amount of reflected light from the surface, and which is used as a criteria for discerning whether the front or reverse side of the paper sheet is being sensed. With this method, precision in sensing may be lowered due to fouling and deflection or vibrations caused during transport as with the first method.
According to a third method, the positions of magnetic ink printing zones are resorted to as the basis for judgment. With the third method, precision in sensing may be affected by strong or weak contact of the magnetic hand with the bank note. In addition, the bank note being sensed may be jammed due to contact with the magnetic head, thus giving rise to malfunction of the device.